This invention is in the field of rotary heat exchangers; more particularly, the invention relates to a rotary heat exchanger core and seals for use in rotary heat exchangers.
Rotary heat exchangers are used to transfer heat from one fluid, such as a gas, to another. Rotary heat exchangers used to transfer heat between gas streams comprise a hot gas directing system, a cold gas directing system, a rotary heat exchanger core, and a means to rotate the core through the hot and cold gas directing systems, continually transferring heat from the hot gas stream to the cold gas stream. Rotary heat exchangers are used with hot and cold gas streams in applications such as turbines and industrial energy recovery systems. The rotating core of the rotary heat exchanger must be properly sealed so that there is no leakage between the hot and cold gas streams.
Generally, the rotary heat exchanger core comprises a central hub and a circumferential frame. There is a matrix of material between the hub and the frame through which the hot and cold gas streams pass as the core rotates. The matrix is designed to maximize the amount of heat which can be withdrawn from the hot gas stream and passed to the cold gas stream during rotation. The matrix is made of a grid of a heat resistant alloy metal which allows the passage of a gas. Rotary heat exchanger cores are also made of ceramic materials. The metallic and ceramic core matrix materials have large surface areas for fast heat transfer.
There are axial and radial flow rotary heat exchangers. In axial rotary heat exchangers, the gases pass axially through a cylindrically shaped rotary heat exchanger core. Cold gas flows axially through one portion of the core while hot gas flows countercurrently through another portion of the core. There are means to seal to prevent leakage between hot and cold gas streams. U.S. Pat. No. 4,105,062 shows the use of a leaf seal to prevent leakage. However, seals used commercially result in as much as ten percent leakage between the hot and cold gas streams.
Rotary heat exchangers with metallic alloy matrixes or ceramic matrixes are known in the art which are used to transfer heat from gases at temperatures as high as 1600.degree. F. A continual problem with rotary heat exchangers particularly used at higher temperatures is thermal fatigue and thermal distortion. This results in warpage of metallic alloy cores and fatigue failures of ceramic cores initially resulting in leakage and finally failure of the core.
Rotary cores, as known in the art, are composed of one cylindrical unit. The core width can vary, as desired. The core diameter can be from about two feet to about twelve feet. Metallic cores are made of stainless steel. A typical stainless steel for high temperature metallic cores is 446 stainless steel having a nominal percent composition of 0.10 C, 1.00 Mn, 0.015 P, 0.015 S, 0.50 Si, 25 Cr, 0.70 (max) Ni, 0.15 N.sub.2 and 73 Fe. The core can be composed of a grid of stainless steel plate having a desired thickness. Typically, the thickness between 0.005 and 0.002 inches with 0.002 inch plate is commonly used.
Various core designs are known in the art. Of interest is the suggestion in U.S. Pat. No. 3,162,241 of a matrix which may be a series of discs. This patent is concerned with rotary heat exchangers in which air passes radially through the matrix. Each disc in this arrangement would see the same thermal gradients. There is no suggestion of overcoming the problems of thermal distortion and dimension change between adjacent discs. Further, it is suggested that if the matrix is made of a series of discs, these discs are assembled in one cylindrical annular framework which is not itself separated into integral discs.
U.S. Pat. No. 3,367,404 discloses a rotary heat exchanger with a ceramic matrix made up of a plurality of discs cemented together. As in the above patent, this patent is directed towards a rotary heat exchanger where the gas passes radially through the matrix. The use of a plurality of discs in this ceramic matrix is directed toward a more economical method of production of the matrices.
Generally, the problems of leakage and warpage resulting from thermal fatigue and thermal distortion are recognized in the art and attempts are continually made to minimize or eliminate these problems. The present invention is an improved rotary heat exchanger core which minimizes or eliminates these problems.